Annunciator system



1944 N. Y. PRIESSMAN ANNUNCIATOR SYSTEM Filed June 26, 1943 lNl/EN TORNJ. PRIESSMAN A TTOPNE Y Patented Nov. 14,

UNITED STATES PATENT OFFICE ANNUNCIATOR SYSTEM Neil Y. Priessman, ShortHills, N. 1., assignor to Bell Telephone Laboratories, Incorporated, NewYork, N Y., a corporation of New York Application June 26, 1943, SerialNo. 492,384

4 Claims.

known as series line lamp lines, 1. e., lines in which a line lamp isconnected in series with the line and li hted without the aid of aso-called line relay and in connection with which a night alarm relaycommon to a plurality of lines are caused to operate whenever any one ofthe lines calls.

Heretofore various arrangements have been suggested and used for givinga night alarm at the central office, as for example by inserting a relayin the common lead between the central ofllce battery and the line lampsor line relays whereby whenever any one of the lines calls, the commonor night alarm relay operates thereby closing a local circuit to light apilot lamp or actuate some other signal device as an indication that acall has been received. Such an arrangement; however, is sometimesundesirable as the cumulative effect of leakage to ground on a number oflines may cause sufficient current to flow in the common relay to causeits operation, thus giving a false indication of a call.

An object of the invention is to insure reliable operation of a nightalarm circuit in response to a call in spite of steady simultaneousleakage to ground from a number of the lines.

A further object is to prevent false operation of a night alarm circuitdue to a. steady and substantial leakage to ground on the lines.

A still further object is to insure reliable operation of a night alarmcircuit when the line current suddenly increases in value a substantialamount.

A feature of the invention whereby the foregoing objects are attainedresides in connecting the primary of a transformer in series with theline signal battery, connecting the usual night alarm relay in a localcircuit, serially including a source of current and a heater typethermistor of the character disclosed in U. S; Patent 2,084,135(resistance l9), and in connecting the heater coil thereof in serieswith the secondary of the transf former, whereby a sudden increase incurrent through the transformer primary winding induces an impulse inthe secondary winding which in passing through the heater winding.raises the temperature of the thermistor sufficiently to reduce itsresistance to the point where the night alarm relay will operate.

An alternative featureof the invention resides in employing anon-inductive resistance element in place of the transformer previouslyreferred to which resistance is connected in series with the batterysupply for the line signals and in connecting the heating coil of thethermistor across the resistance and battery in series with a condenserof substantial capacity whereby the condenser is normally charged to thepotentials of battery and discharges through the heating coil of thethermistor when a sudden change in current, through the resistance,occurs due to a call on one of the lines, the capacity of the condenserbeing the heating coil is sufficient to reduce the thermistor resistanceand permit operation of the night alarm.

The invention will be understood from the following description andaccompanying drawing, Fig. 1 of which represents a night alarmarrangement employing a transformer for heating the thermistor inaccordance with the first feature, and Fig. 2 represents the arrangementof the alternative feature which employs a resistance element in placeof a transformer.

In Fig. 1' a subscriber's telephone line L1 is shown terminating at oneend in a switchboard jack I and-at the other end in a subscriber'stelephone station T. Other telephone lines L2 and La extend from otherswitchboard jacks 2 and 3 to 'othersubscribers stations, not shown.

The plug 4. of an operators cord is adapted to.

be connected with any of the lines.

The tip side of line L1 (for example) is connected to ground throughcontacts 5 of jack l and L: are connected in a similar manner throughtheir respective line lamps l0 and I l to the common conductor 8 andthence to battery through the transformer 9.

It will be understood that other line lamps can be connected to theconductor 8 in a similar manner.

Connected to the secondary of transformer 9 is a circuit including aheating winding I2 in close proximity to a so-called thermistor ornegative temperature resistance element I-3 which is serially connectedin the energizing circuit of the night alarm relay l4 whose armature andcontacts control a'signal device such asa bell I5.

It will be understood that the thermistor I3 is of such a character andso chosen that its normal or cold resistance is such that it will notpass so chosen that the discharge current through I but when itstemperature is raised to a predetermined value its resistance willdecrease to a point where the relay l4 will receive the requiredoperating current As previously indicated one or more of the lines mayhave high resistance ground (or crosses) due to faulty insulation Orother causes and if such grounds are present on the ring conductor ofthe line, as indicated at IS, IT and I8, there will be a multipleleakage path for current from the battery B through the line lamps ofthe grounded lines and while the leakage current through a single linelamp may be insuflicient cause it to glow with visible brilliancy thecombined leakage current of several grounded lines may be as great orgreater than the current required to light one of the lamps to fullbrilliancy but as the night alarm relay it, instead of being connectedin series with the battery and line lamp, as in previous systems, isinductively coupled to the battery supply conductor 8 by means of thetransformer 9 and the leakage current seldorn is subject to rapidfluctuation, this relay remains inert with its contacts in their open ornormal condition due to the cold (high) resistance of the thermistor l3.

In case station T, for example, calls by lifting the receiver from thehook, a sudden increase occurs in the current flowing in the primarywinding of the transformer thereby inducing a current in the secondarywinding which flows in the heater winding i2 thus raising thetemperature of the thermistor thereby lo,.-:ing its resistance whereuponrelay H operates to actuate the alarm mil it. i

When the temperature of thermistor I 3 has been raised to the pointwhere sufficient current flows to operate relay i4, this current will,due to the resistance of; the thermistor, maintain it at its conductingtemperature thus holding the relay operated until released by operationof release key RK.

Fig, 2 shows an auxiliary arrangement for accomplishing the same resultas in Fig. 1 and is adapted to be connected to conductor 8 thereof in anobvious manner and consists of a noninductive resistance l9 connected inseries with the battery B, and a circuit for the heater winding i2serially including a condenser 20 which circuit is connected across theresistance and battery in the manner shown so that condenser 20 will benormally charged to the full potential of the battery or to thatpotential less the drop in resistance l9 due to leakage current on thelines and hence no current fiows in the heater winding l2. When,however, a line calls a sudden drop in potential occurs acrossresistance l9, due to the line lamp current which causes a change in thepotential of condenser 20 and a consequent momentary flow of current inthe heating coil I! which, as before, permits relay H to operate.

What is claimed is:

1. In a telephone system, a central oflice, a plurality of linesterminating thereat, a signal device in series with each line at saidcentral ofllce, a common source of current at said central ofllce forenergizing said signals, a night alarm relay at the central omce, acircuit for said relay serially including a source of current and aresistance element having a negative temperature coeflicient, anelectrical heater for raising the temperature of said negativetemperature element and a transformer having a primary and a secondarywinding and connected with its primary winding in series with saidcentral office current source and its secondary winding connected tosaid electrical heater.

2. In a signaling system, a signal, an energizing circuit therefor, atransformer having a primary winding in said energizing circuit, arelay, an energizing circuit therefor including a source of current anda resistance having a negative temperature coefficient, an electricalheater for raising the temperature of said resistance and a circuit forsaid heater serially including a secondary winding of said transformerwhereby a sudden change in current in said signal energizing circuitwill cause a current impulse to flow in said heater to raise itstemperature and that or its associated resistance to reduce theresistance of said relay circuit and cause its operation.

3. In a telephone system, a central ofllce, a plurality of linesterminating thereat, a signal device in series with each line at saidcentral ofllce, a common source of current at said central ofllce forenergizing said signals, a night alarm relay at the central ofllce, acircuit for said relay, serially including a source of current and aresistance element having a negative temperature coemcient, anelectrical heater for raising the temperature of said resistanceelement, impedance means in series with said common source of current,and circuit means interconnecting said impedance means and said heaterwhereby a sudden increase in potential across said impedance will causea flow of current in said heater.

4. In a telephone system, a central cflice, a plurality of linesterminating thereat, a signal device in series with each line at saidcentral office, a common source of current at said central ofilce forenergizin said signals, a night alarm relay at the central omce, acircuit for said relay serially including a source of current and aresistance element having a negative temperature coefllcient, anelectrical heater for raising the temperature of said resistance elementimpedance means in series with said common source of current and circuitmeans including a condenser interconnecting said impedance means andsaid heater whereby a sudden increase in p0- o0 tential across saidimpedance will cause a flow 0! current in said heater.

NEIL Y. PRIESSMAN.

